Measured the fracture toughness of sun-leaves of 42 tropical tree species growing in Singapore; 37 of the species were from three definable plant communities, namely mangroves, trema belukar (secondary forest on undegraded sites) and adinandra belukar (secondary forest on highly degraded soils). There was a highly significant positive correlation between fracture toughness and index of sclerophylly for the 42 species, brought about largely by a high correlation between toughness and crude fibre content. -from Authors